As an expert on international law, constitutional law, political and legal theory, and jurisprudence, MacKinnon focuses on the issues of sex equality, women's rights, and gender crime, specifically sexual abuse and exploitation, including sexual harassment, rape, prostitution, sex trafficking, and pornography. Professor MacKinnon is also a widely recognized public intellectual on issues involving inequality.

MacKinnon is the Elizabeth A. Long Professor of Law at the University of Michigan Law School[2] and the James Barr Ames Visiting Professor of Law at Harvard Law School. In 2007, she served as the Roscoe Pound Visiting Professor of Law at Harvard Law School[3] and has also visited at NYU, University of Western Australia, University of San Diego, Hebrew University, Columbia Law School, University of Chicago, University of Basel, Yale Law School, Osgood Hall Law School, UCLA School of Law, and Stanford Law School.

MacKinnon is a highly cited legal scholar.[4][5] She regularly appears in public speaking events. On February 10, 2005, she attended the premiere of Inside Deep Throat (for which she was featured as an interviewee) and took part in a panel discussion after the film.[6][7][8][9]

Concretely, MacKinnon's ideas may be divided into three central—although overlapping and ongoing—areas of focus: sexual harassment, pornography and prostitution, and international work. She has also written extensively on social and political theory and methodology.[11]

According to an article published by Deborah Dinner in the March/April 2006 issue of Legal Affairs, MacKinnon first focused on the reality of what became termed sexual harassment after learning about an administrative assistant at Cornell University who had resigned after being hospitalized due to the consequences of sexual harassment and refused a transfer when she complained of her supervisor's harassing behavior, and then was denied unemployment benefits because she quit for what were termed "personal" reasons.

In 1977, MacKinnon graduated from Yale Law School after having written a paper on sexual harassment for Professor Thomas I. Emerson arguing that it was a form of sex-based discrimination. Two years later, Yale University Press published MacKinnon's book, "Sexual Harassment of Working Women: A Case of Sex Discrimination", creating the legal claim for sexual harassment as a form of sex discrimination under Title VII of the Civil Rights Act of 1964 and any other sex discrimination prohibition. While working on the paper and book, she shared draft copies with legal authorities who embraced her approach. She also conceived the legal claim for sexual harassment as sex discrimination in education under Title IX, which was established through litigation brought by Yale undergraduates in Alexander v. Yale. While the plaintiff who went to trial on the facts, Pamela Price, lost, the case established the law: the U.S. Court of Appeals for the Second Circuit recognized that, under the civil rights statute Title IX of the Education Amendments of 1972, schools must have procedures to address sexual harassment as a form of sex discrimination.[12]

In her book, MacKinnon argued that sexual harassment is sex discrimination because the act is a product of, and produces, the social inequality of women to men (see, for example, pp. 116–18, 174). She distinguishes between two types of sexual harassment (see pp. 32–42): 1) "quid pro quo", meaning sexual harassment "in which sexual compliance is exchanged, or proposed to be exchanged, for an employment opportunity (p. 32)" and 2) the type of harassment that "arises when sexual harassment is a persistent condition of work (p. 32)". In 1980, the Equal Employment Opportunity Commission followed MacKinnon's framework in adopting guidelines prohibiting sexual harassment by prohibiting both quid pro quo harassment and hostile work environment harassment (see 29 C.F.R. § 1604.11 (a)). Courts also used the concepts.

In 1986, the Supreme Court held in Meritor Savings Bank v. Vinson that sexual harassment may violate laws against sex discrimination. MacKinnon was co-counsel for Mechelle Vinson, the plaintiff, and wrote the brief in the Supreme Court. In Meritor, the Court recognized the distinction between quid pro quo sexual harassment and hostile workplace harassment. In a 2002 article, MacKinnon wrote, quoting the Court:

"Without question," then-Justice Rehnquist wrote for a unanimous Court, "when a supervisor sexually harasses a subordinate because of the subordinate's sex, that supervisor "discriminate[s]" on the basis of sex." The D.C. Circuit, and women, had won. A new common law rule was established.[13]

MacKinnon's book, Sexual Harassment of Working Women: A Case of Sex Discrimination, is the eighth most-cited American legal book published since 1978, according to a study published by Fred R. Shapiro in January 2000.[14]

MacKinnon, along with late feminist activist Andrea Dworkin, has been active in attempting to change legal approaches to pornography by framing it as a form of sex discrimination and, more recently, a form of human trafficking. She and Dworkin define pornography as follows

We define pornography as the graphic sexually explicit subordination of women through pictures and words that also includes (i) women are presented dehumanized as sexual objects, things, or commodities; or (ii) women are presented as sexual objects who enjoy humiliation or pain; or (iii) women are presented as sexual objects experiencing sexual pleasure in rape, incest or other sexual assault; or (iv) women are presented as sexual objects tied up, cut up or mutilated or bruised or physically hurt; or (v) women are presented in postures or positions of sexual submission, servility, or display; or (vi) women's body parts—including but not limited to vaginas, breasts, or buttocks—are exhibited such that women are reduced to those parts; or (vii) women are presented being penetrated by objects or animals; or (viii) women are presented in scenarios of degradation, humiliation, injury, torture, shown as filthy or inferior, bleeding, bruised, or hurt in a context that makes these conditions sexual.

In Toward a Feminist Theory of the State, MacKinnon writes, "Pornography, in the feminist view, is a form of forced sex, a practice of sexual politics, and institution of gender inequality." As documented by extensive empirical studies, she writes, "Pornography contributes causally to attitudes and behaviors of violence and discrimination which define the treatment and status of half the population."[15]:196

In 1980, Linda Boreman (who had appeared, under the name Linda Lovelace in the pornographic film Deep Throat) claimed her ex-husband Chuck Traynor had violently coerced her into making Deep Throat and other pornographic films. Boreman made her charges public for the press corps at a press conference, together with MacKinnon, members of Women Against Pornography, and feminist writer Andrea Dworkin offering statements in support. After the press conference, Dworkin, MacKinnon, Boreman, and Gloria Steinem began discussing the possibility of using federal civil rights law to seek damages from Traynor and the makers of Deep Throat. This was not possible for Boreman because the statute of limitations for a possible suit had passed.[16]

MacKinnon and Dworkin continued to discuss civil rights litigation, specifically sex discrimination, as a possible approach to combating pornography. MacKinnon opposed traditional arguments and laws against pornography based on the idea of morality or filth or sexual innocence, including the use of traditional criminal obscenity law to suppress pornography. Instead of condemning pornography for violating "community standards" of sexual decency or modesty, they characterized pornography as a form of sex discrimination and sought to give women the right to seek damages under civil rights law when they could prove they had been harmed. Their anti-pornography ordinances make actionable only sexually explicit material that can be proven to subordinate on the basis of sex.

In 1983, the Minneapolis city government hired MacKinnon and Dworkin to draft an anti-pornography civil rights ordinance as an amendment to the Minneapolis city human rights ordinance. The amendment defined pornography as a civil rights violation against women and allowed women who claimed harm from trafficking in pornography to sue the producers and distributors for damages in civil court. It also allowed those who had been coerced into pornography, had had pornography forced upon them, or were assaulted in a way caused by specific pornography to sue for harm they could prove. The law was passed twice by the Minneapolis city council but was vetoed by the mayor. Another version of the ordinance passed in Indianapolis, Indiana in 1984, but was ruled unconstitutional by the Seventh Circuit Court of Appeals, a decision summarily affirmed (without opinion) by the U.S. Supreme Court.

MacKinnon wrote in the Harvard Civil Rights-Civil Liberties Law Review in 1985

And as you think about the assumption of consent that follows women into pornography, look closely some time for the skinned knees, the bruises, the welts from the whippings, the scratches, the gashes. Many of them are not simulated. One relatively soft core pornography model said, "I knew the pose was right when it hurt." It certainly seems important to the audiences that the events in the pornography be real. For this reason, pornography becomes a motive for murder, as in "snuff" films in which someone is tortured to death to make a sex film. They exist."[17]

MacKinnon represented Boreman from 1980 until Boreman's death in 2002. Civil libertarians frequently find MacKinnon's theories objectionable (see "Criticisms" section), arguing there is no evidence that sexually explicit media encourages or promotes violence against, or other measurable harm of women.[18] Max Waltman states that the empirical evidence for this view is emphatic.[19]

In February 1992, the Supreme Court of Canada largely accepted MacKinnon's theories of equality, hate propaganda, and pornography, citing extensively from a brief she co-authored in a ruling againstManitoba pornography distributor Donald Butler. The Butler decision was controversial to some; it is sometimes implied that shipments of Dworkin's book Pornography: Men Possessing Women were seized by Canadian customs agents under this ruling, as well as books by Marguerite Duras and David Leavitt.[20][21] In fact, MacKinnon's brief argued that seizure of materials for which no harm was shown was unconstitutional.

Successful Butler prosecutions have been undertaken against the lesbiansadomasochistic magazine Bad Attitude, as well as the owners of a gay and lesbian bookstore for selling it. Canadian authorities raided an art gallery and confiscated controversial paintings depicting child abuse. Many free speech and gay rights activists have alleged that the law is selectively enforced, targeting the LGBT community.

MacKinnon represented Bosnian and Croatian women against Serbs accused of genocide since 1992, creating the legal claim for rape as an act of genocide in that conflict. She was co-counsel, representing named plaintiff S. Kadic, in Kadic v. Karadzic and won a jury verdict of $745 million in New York City on August 10, 2000. The lawsuit (under the United States' Alien Tort Statute) established forced prostitution and forced impregnation when based on ethnicity or religion in a genocidal context as legally actionable acts of genocide.[22] In 2001, MacKinnon was named co-director of the Lawyers Alliance for Women (LAW) Project, an initiative of Equality Now, an international non-governmental organization.[23]

MacKinnon proposed the law against prostitution in Sweden in 1990, which Sweden passed in 1999. What became termed the Swedish Model, also known as the Nordic Model or the Equality Model, penalizes buyers of persons for sexual use as well as sellers, namely pimps or sex traffickers, while decriminalizing all those who are bought and sold in prostitution. The fundamental concept is that the requirement to exchange sexual use for survival is a product of sex inequality and a form of violence against women. This model, shown to have reduced prostitution and sex trafficking dramatically, has been accepted in Norway, Iceland, Canada, Ireland, Northern Ireland, and France. (citation needed) MacKinnon works actively with the Coalition Against Trafficking in Women (CATW) and Apne Aap in India.

MacKinnon argues that the inequality between women and men in most societies form a hierarchy that institutionalizes male dominance, subordinating women, in an arrangement rationalized and often perceived as natural.

MacKinnon writes about the interrelations between theory and practice, recognizing that women's experiences have, for the most part, been ignored in both arenas. Furthermore, she uses Marxism to critique certain points in liberal feminism in feminist theory and uses feminism, namely, radical feminism to criticize Marxist theory[24]. MacKinnon notes Marx's criticism of theory that treated class division as a spontaneous event that occurred naturally. She understands epistemology as theories of knowing and politics as theories of power. She explains, "Having power means, among other things, that when someone says, 'this is how it is', it is taken as being that way. ... Powerlessness means that when you say 'this is how it is,' it is not taken as being that way. This makes articulating silence, perceiving the presence of absence, believing those who have been socially stripped of credibility, critically contextualizing what passes for simple fact, necessary to the epistemology of a politics of the powerless."[25][15]

In 1996, Fred R. Shapiro calculated that "Feminism, Marxism, Method, and the State: Toward Feminist Jurisprudence", 8 Signs 635 (1983), was the 96th most cited article in law reviews even though it was published in a non-legal journal.[26]

During the "Feminist Sex Wars" in the 1980s, feminists opposing anti-pornography stances, such as Carole Vance and the late Ellen Willis, began referring to themselves as "pro-sex" or "sex-positive feminists". Sex positive feminists and anti-pornography feminists have debated over the implicit and explicit meanings of these labels. Sex-positive feminists note that anti-pornography ordinances contrived by MacKinnon and Dworkin called for the removal, censorship, or control over sexually explicit material.[27]

In States of Injury (1995), Wendy Brown contends that MacKinnon's attempt to ban prostitution and pornography does not primarily protect but reinscribes the category of "woman" as an essentialized identity premised on injury.[28] In The Nation, Brown also characterized MacKinnon's Toward a Feminist Theory of the State (1989) as a "profoundly static world view and undemocratic, perhaps even anti-democratic, political sensibility" as well as "flatly dated" and "developed at 'the dawn of feminism's second wave ... framed by a political-intellectual context that no longer exists—a male Marxist monopoly on radical social discourse'".[29]

MacKinnon, Catharine A. (Harvard University Press, 1987). Feminism Unmodified: Discourses on Life and Law

MacKinnon, Catharine A. & Dworkin, Andrea (Organizing Against Pornography, 1988). Pornography and Civil Rights: A New Day for Women's Equality

MacKinnon, Catharine A. (Harvard University Press, 1989). Toward a Feminist Theory of the State

MacKinnon, Catharine A., Mary A. Eberts, et al. (Federation of Women Teachers’ Associations of Ontario, 1991). The Case for Women's Equality: The Federation of Women Teachers' Associations of Ontario and the Canadian Charter of Rights and Freedoms

^Dworkin, Ronald. "Women and Pornography", New York Review of Books 40, no. 17 (21 October 1993): 299. "no reputable study has concluded that pornography is a significant cause of sexual crime: many of them conclude, on the contrary, that the causes of violent personality lie mainly in childhood"

^Waltman, Max (March 2010). "Rethinking Democracy: Legal Challenges to Pornography and Sex Inequality in Canada and the United States". Political Research Quarterly. 63: 218–237.